The subject matter disclosed herein relates to X-ray tube radiation sources and more particularly to X-ray tube radiation sources having gridding electrodes.
In imaging systems, X-ray tubes are used in projection X-ray systems, fluoroscopy systems, tomosynthesis systems, and computer tomography (CT) systems as a source of X-ray radiation. Typically, the X-ray tube includes a cathode and an anode. The cathode emits a stream of electrons in response to heat resulting from an applied electrical current via the thermionic effect. The anode includes a target that is impacted by the stream of electrons. The target, as a result, produces X-ray radiation and heat. Such systems are useful in medical contexts, but also for parcel and package screening, part inspection, various research contexts, and so forth.
The radiation traverses a subject of interest, such as a human patient, and a portion of the radiation impacts a detector or photographic plate where the image data is collected. In some X-ray systems, the photographic plate is then developed to produce an image which may be used by a radiologist or attending physician for diagnostic purposes. In digital X-ray systems, a photo detector produces signals representative of the amount or intensity of radiation impacting discrete pixel regions of a detector surface. The signals may then be processed to generate an image that may be displayed for review. In CT and tomosynthesis systems, a detector array, including a series of detector elements, produces similar signals through various positions as a gantry is displaced around a patient, and processing techniques are used to reconstruct a useful image of the subject.
In certain imaging systems (e.g., CT systems), the X-ray tube may be utilized in a variety of dynamic focal spot modes. During these dynamic focal spot modes, the imaging system may switch between different focal spot positions (e.g., during focal spot wobbling), different focal spot sizes or shapes, different peak kilovoltages applied across the X-ray tube, different milliamperes applied across the X-ray tube, or a combination there. These transitions or switches during the dynamic focal spot mode may result in damage to the X-ray tube due to focal spot instability or variation and, thus, a shortened X-ray tube life. For example, too large an electron beam (e.g., resulting in damage to beam pipe or other internal apertures thru which the electron beam travels en route to the target) or too small an electron beam (e.g., resulting in target overheating) may result in X-ray tube damage. In addition, focal spot instability may result in reduced image quality due to the acquisition of focal spot artifacts. Further, in an effort to avoid exceeding a temperature limit of the target (e.g., anode) due to overheating or re-heating during the dynamic focal spot mode, the beam power and, thus, the X-ray flux may be limited.